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Atomic Theory
Agenda
New elements
Grade tests
Guided reading of chp 4
Song about Atomic Theory
Notes on Atomic Theory
Song Time
Atomic Theory Polka
• Dalton, Thomson, Rutherford and Bohr.
Schrödinger and Heisenberg, and many, many
more. Used their brains to venture in the
realm of inner space and found the world of
the atom was a weird and wondrous place.
• Dalton did experiments and said, “I think it’s
clear, atoms are tiny indestructible spheres.”
• Thomson worked with cathode rays and said,
“I disagree. A plum-pudding model makes
much more sense to me.”
• A new chapter in atomic theory started to
unfold when Rutherford played around with
atoms made of gold. When a few of his alpha
particles came bounding back, he
hypothesized a nucleus had knocked them off
the track.
• Dalton, Thomson, Rutherford and Bohr.
Schrödinger and Heisenberg, and many, many
more. Used their brains to venture in the
realm of inner space and found the world of
the atom was a weird and wondrous place.
• Bohr saw spectral lines for hydrogen and said,
“It seems to me.. Electrons move in orbits
with specific energies.”
electron
neutron
proton
• Heisenberg said, “Forget it, there’s no way to
know the orbit or a path, where the electron’s
gonna go.”
• Schrödinger used lots and lots of fancy
mathematics, and made a model of the atom
based on quantum mechanics. It has orbitals
and those are based on probability. The atom
is a fuzzy blob of pure uncertainty.
• Dalton, Thomson, Rutherford and Bohr.
Schrödinger and Heisenberg, and many, many
more. Used their brains to venture in the
realm of inner space and found the world of
the atom was a weird and wondrous place.
Atomic Theory
Date
Democritus
• Date 460-370 B.C.
• Democritus was a philosopher; did no
research
• He thought that everything was made up
of tiny round things called atoms.
• Atoms are the building blocks of life.
John Dalton
• 1787 – 1844
• Wanted to learn in what ratios different
elements combine in chemical reactions.
• Through experimentation devised his atomic
theory.
Dalton’s Atomic Theory
1. Elements are composed of submicroscopic
indivisible particles called atoms.
2. All atoms of a given element are identical. Atoms
of different elements are different from one
another.
3. Atoms of one element can mix or chemically
combine with atoms of other elements, creating
compounds with simple whole-number ratios.
4. Chemical reactions occur when atoms are
separated, joined or rearrange.
JJ Thomson
•
•
•
•
Found electron
Used cathode ray tube
“Plum Pudding” or “Chocolate Chip Cookies” model
video of cathode ray bending
http://tinyurl.com/6laasks
Robert Millikan
• Determined the electrical charge of electron
• “Oil Drop Experiment” – like a balloon attracting a
bubble up while gravity pulls bubble down.
• Still plum pudding model
Eugen Goldstein
• Found the proton
• Reverse cathode ray tube
• Still plum pudding model
Ernest Rutherford
• Found nucleus
• Gold foil experiment
• Atom is mostly empty space – first nuclear model
James Chadwick
• Found neutron
• Shot alpha particles at Be nucleus
• Nucleus is made of two particles
– Positive protons
– Neutral neutrons
Niels Bohr
• Planetary model
• Proposed electrons have a set amount of energy putting them
in different energy levels, or orbits around the nucleus.
• Electrons can change energy levels; higher energy levels are
further from the nucleus.
electron
neutron
proton
Heisenberg’s uncertainty principle
• Heisenberg’s uncertainty principle: cannot
know exactly both the velocity and position of
electron at the same time.
• Like trying to catch a helium balloon in the
dark.
Schrödinger
• Electron cloud gives a 90% probability of
finding the electron within the darkly shaded
area.
• Electrons move like moths around a light –
unpredictable.